Virus-induced apoptosis is important in the pathogenesis of viral diseases, especially those of the central nervous system and AIDS. While several cellular and virally-encoded inhibitors of virus-induced apoptosis have been identified, little is known about how anti-apoptotic genes function in vivo to regulate viral pathogenesis. The broad. long term objective of this project is to elucidate cellular mechanisms involved in the regulation of virus-induced apoptosis and viral pathogenesis, by focusing on the role of the prototypic cell death inhibitor, Bcl-2, and a recently identified novel Bcl-2 interacting candidate tumor suppressor protein. Beclin, in the pathogenesis of Sindbis virus encephalitis. Sindbis virus, the type alpha-virus, is a single-stranded RNA virus that causes an age-dependent fatal encephalitis in mice and serves as an animal model for human arthropod- borne encephalitides. The two major specific aims of this proposal are: (1) to define the role of Bcl-2 and Beclin in protection against Sindbis virus-induced apoptosis and disease; and (2) to investigate mechanisms by which Bcl-2 and Beclin protect against fatal Sindbis virus encephalitis. Under the first aim, we will investigate the hypotheses that endogenous bcl-2 and endogenous beclin play a role in protection against Sindbis virus-induced neuronal death and fatal Sindbis virus encephalitis. Under the second specific aim, we will investigate the hypotheses that (1) Beclin-Bcl-2 interactions are important in protection against fatal Sindbis virus encephalitis; (2) that neuronal Bcl-2 and Beclin have antiviral activity that is linked to anti- apoptotic activity and protection against fatal Sindbis virus encephalitis; and (3) that negative cell cycle regulatory effects of Bcl-2 and/or Beclin are important for protection against fatal Sindbis virus encephalitis. To accomplish these aims, we will use in vivo model systems employing beclin-1- and bcl-2-/- mice and an in vitro model system employing dorsal root ganglion neurons explanted from such mice, in conjunction with our previously established Sindbis virus vector system, for expressing wild-type and mutant forms of death regulatory genes in neurons. The research design will involve manipulation of these models to critically evaluate the central hypotheses of the application. The proposed studies will provide novel insights into host cellular mechanisms that regulate whether neurons live or die in responses to viral infection.